The present invention relates to electrically addressable displays and, more particularly, to an electrically addressable liquid crystal display system comprising a circuit board and a display sheet on a flexible substrate, the circuit board and display sheet being aligned by reference features such as pins and corresponding holes.
Images can be displayed on ink-bearing sheets of paper or on various electronically modulated surfaces such as cathode ray displays or liquid crystal displays, the latter comprising liquid crystalline materials that can be manipulated between light scattering and light transmissive modes in response to applied electric fields. Liquid crystalline materials, which may have either positive or negative dielectric anisotropy, are generally classified as nematic or smectic. A particular type of nematic liquid crystals, referred to as chiral nematic, has the ability to selectively reflect one component of circularly polarized light. In the chiral nematic phase, which is synonymous with the cholesteric phase, chiral molecules form very thin layers of aligned molecules, the alignment in one layer being at a slight angle from that in an adjacent layer, and the alignment in a stack of such layers forming a continuous helical pattern.
Many known liquid crystal display devices make use of liquid crystalline materials dispersed in polymeric matrices. For example, U.S. Pat. No. 4,435,047, the disclosure of which is incorporated herein by reference, describes a liquid crystalline material, preferably nematic, of positive dielectric anisotropy dispersed in a polymeric encapsulating medium such as polyvinyl alcohol. Also, U.S. Pat. No. 4,685,771, the disclosure of which is incorporated herein by reference, describes a light-modulating liquid crystal display material that contains liquid crystalline microdroplets dispersed in a thermoplastic resin, the microdroplets being of a size effective to scatter incident light when the optical axes of the microdroplets are randomly aligned. U.S. Pat. No. 5,116,528, the disclosure of which is incorporated herein by reference, describes a light modulating material that includes a liquid crystalline material dispersed in a cross-linked isocyanate material, preferably a polyacrylic urethane. Also, U.S. Pat. No. 5,583,670, the disclosure of which is incorporated herein by reference, describes an information recording layer in which a liquid crystal phase is dispersed in an acrylic or methacrylic resin having a molecular weight of 25,000 to 100,000.
PCT/WTO 97/04398, entitled ELECTRONIC BOOK WITH MULTIPLE DISPLAY IMAGES, discloses the assembly of multiple electronically written display sheets into a xe2x80x9cbook.xe2x80x9d The reference describes prior art techniques for forming thin, electronically written pages, including flexible sheets, image modulating material formed from a bi-stable liquid crystal system, thin metallic conductor lines on each page, and transparent conducting polymers formed over the light modulating material.
Co-pending, commonly assigned U.S. application Ser. No. 09/379,776, filed Aug. 24, 1999 for FORMING A DISPLAY HAVING CONDUCTIVE IMAGE AREAS OVER A LIGHT MODULATING LAYER, the disclosure of which is incorporated herein by reference, describes a method for forming a display on a transparent substrate on which is formed a transparent, electrically conductive coating. A light modulating layer including liquid crystalline material in a polymer binder is formed over the electrically conductive layer, and an opaque conductive material is deposited in an imagewise pattern over the light modulating layer in the form of viewable and conductive images. The light modulating layer is effective in a first condition to prevent the viewing of the viewable and conductive images and in a second condition to permit the viewing of the viewable and conductive images. Electrical connections enable an electrical field to be applied across selected ones of the viewable and conductive images and the transparent electrically conductive layer to cause the light modulating layer underlying the selected images to change from the first condition to the second condition and thereby present the images for viewing by a viewer.
Display systems, in particular, matrixed displays typically have a large number of conductive traces for addressing the individual pixel elements comprising the display. These conductive traces are electrically connected to a circuit board on which control driver chips for the display are mounted.
Accurately aligning the many fine conductive traces to the corresponding conductive contacts on the circuit board is a difficult process, which, however, is substantially facilitated by the present invention
The present invention is directed to an electrically addressable display system that includes a circuit board and at least one flexible display sheet disposed above and electrically connected with the circuit board. The surface of the circuit board includes first electrically conductive contacts and at least one first reference feature disposed at a selected position in relation to the first contacts. The display sheet includes second electrically conductive contacts disposed on a transparent flexible substrate and at least one second reference feature disposed at a selected position in relation to the second contacts. The second reference feature of the display is in vertical alignment with the first reference feature of the circuit board, thereby providing for alignment of the first electrically conductive contacts on the circuit board with the second electrically conductive contacts on the display sheet.
The present invention is further directed to an electrically addressable liquid crystal display system that includes a circuit board and at least one liquid crystal display sheet electrically connected with the circuit board. A surface of the circuit board includes a first array of parallel conductive contacts and a second array of parallel conductive contacts. The second array is orthogonally disposed to the first array, and each array is bounded by two parallel edges. Two reference pins, each disposed at a selected distance from one of the conductive contact array edges and from one another, protrude from the circuit board surface.
The flexible liquid crystal display sheet disposed above and electrically connected with the circuit board includes a transparent flexible substrate, a transparent first electrically conductive layer comprising a first array of parallel conductive traces bounded by two parallel edges disposed on the substrate, a light modulating layer comprising a liquid crystalline material dispersed in a polymeric binder disposed on the first electrically conductive layer, and a second electrically conductive layer comprising a second array of parallel conductive traces bounded by two parallel edges disposed on the light modulating layer. The conductive trace arrays are orthogonally disposed to each other, and each of the conductive traces in the arrays is in electrical communication with a conductive contact in the contact arrays, thereby defining rows and columns of pixels.
The liquid crystal display sheet further includes two reference holes through the display. Each of the holes is disposed at a selected distance from one of the conductive trace array edges and from one another, and each hole is in vertical alignment with and engaged with a corresponding pin on the underlying circuit board. The arrays of conductive contacts on the circuit board are thereby aligned with the arrays of conductive traces on the liquid crystal display sheet.
The present invention is further directed to a process for forming an electrically addressable liquid crystal display system that comprises: providing a circuit board having a surface comprising a first array of parallel conductive contacts and a second array of parallel conductive contacts orthogonally disposed to the first array, each of the arrays being bounded by two parallel edges; and two reference pins protruding from the surface, each of the pins being disposed at a selected distance from one of the conductive contact array edges and from one another. Further provided is at least one liquid crystal display sheet comprising a flexible substrate, a transparent first electrically conductive layer comprising a first array of parallel conductive traces bounded by two parallel edges disposed on the substrate, a light modulating layer comprising a liquid crystalline material dispersed in a polymeric binder disposed on the first electrically conductive layer, and a second electrically conductive layer comprising a second array of parallel conductive traces bounded by two parallel edges disposed on the light modulating layer. The conductive trace arrays are orthogonally disposed to each other, and each of the traces in the arrays is in electrical communication with a conductive contact in the contact arrays, thereby defining rows and columns of pixels.
The process of the invention further comprises: forming two reference holes through the liquid crystal display sheet, each of the holes being disposed at a selected distance from one of the conductive trace array edges and from one another; and positioning the liquid crystal display on the circuit board to cause the pins to be in vertical alignment with and to engage the holes. The arrays of conductive contacts on the circuit board are thereby aligned with the arrays of conductive traces on the liquid crystal display.